A standard track chain, such as described in U.S. Pat. No. 4,179,130, is formed of a succession of links each consisting of a pair of parallel link elements extending along the track displacement direction, a pin extending perpendicular to this direction from one end of one of the link elements to the corresponding one end of the other link element, and a sleeve or tube extending between the other ends of the link elements parallel to the pin. The one ends interconnected by the pin are further apart than the other ends interconnected by the sleeve, and each pin passes through the sleeve of the leading or trailing link. Thus the links are journaled together by the pins fitting in the sleeves at a joint capable of transmitting considerable force while relatively inexpensive to mass produce.
Obviously it is essential to keep the space between each sleeve and the pin it receives perfectly clean and well lubricated, to minimize wear at this sliding-surface joint. Accordingly a seal is provided that is compressed axially between each end face of the sleeve and a confronting end face of the respective one link end. This seal must keep the lubricant in while keeping liquids and grit out, a particularly difficult task due to the inevitable use of the track chain in wet and dirty conditions.
The seal is formed of a deformable but relatively wear-resistant U-section outer part and an elastomeric and very springy inner part within the outer part and biasing same into axial contact with both the end faces. To this end the axially oppositely directed sides of the seal are formed with outwardly directed ridges or lips to provide line contact between the seal and the surfaces engaged by it. The inner part according to the above-mentioned patent is formed of steel and of U-section like the outer part, but is fitted into it so the it opens at the base of the outer part. The legs of the inner and outer parts therefore bear axially on each other.
A problem with such a seal is that it can get canted in the recess, lifting partially from one or the other end surfaces. This allows leakage into and out of the link assembly. In addition the somewhat exposed steel inner part of the seal is relatively corrosible, so it must be replaced often, in particular when used around salt water. Since the seal is a fairly expensive item, such replacement can be quite costly.